Dielectric Properties Of Aqueous Solutions Research Articles

Dielectric properties of aqueous solutions of the ammonium heptamolybdate-poly(vinyl alcohol)-water system

The microwave dielectric properties of aqueous solutions of the ammonium heptamolybdate (AHM)-poly(vinyl alcohol)-water ((NH4)6Mo7O24-PVA-water) system are studied along sections with constant concentrations of the components in the frequency region in which the dispersion peak of the dielectric constant of water falls (13–25 GHz) at 298 and 313 K. The static dielectric constant es and the dielectric relaxation time τ of the solutions are found. The dielectric characteristics along the sections vary additively as a function of concentration with respect to the relationships observed in the AHM-water and PVA-water binary systems. The rotational mobility of water molecules is mainly controlled by polymer additives. We suggest that two (water and polymer-ion) subsystems exist in the solution in this case; these subsystems only weakly affect each other.

Dielectric Properties of Solutions Isomorphous with Water

The dielectric properties of aqueous solutions of ammonia, hydrogen fluoride, hydrogen peroxide, and ammonium halides are determined by the number of hydrogen bonds formed by the solute species with the molecules forming the water framework. For such solutions, the product of the concentration coefficient of the dielectric permittivity by the ratio of the number of hydrogen bonds per solute molecule and per water molecule is constant. In aqueous solutions with a water-like structure, the mechanism of the dielectric polarization is the same as in pure water (proton-activation mechanism) and is determined by proton fluctuations on the line of hydrogen bonds.

A molecular dynamics study of the dielectric properties of aqueous solutions of alanine and alanine dipeptide.

Molecular dynamics simulations were used to compute the frequency-dependent dielectric susceptibility of aqueous solutions of alanine and alanine dipeptide. We studied four alanine solutions, ranging in concentration from 0.13-0.55 mol/liter, and two solutions of alanine dipeptide (0.13 and 0.27 mol/liter). In accord with experiment we find a strong dielectric increment for both solutes, whose molecular origin is shown to be the zwitterionic nature of the solutes. The dynamic properties were analyzed based on a dielectric component analysis into solute, a first hydration shell, and all remaining (bulk) waters. The results of this three component decomposition were interpreted directly, as well as by uniting the solute and hydration shell component to a "suprasolute" component. In both approaches three contributions to the frequency-dependent dielectric properties can be discerned. The quantitatively largest and fastest component arises from bulk water [i.e., water not influenced by the solute(s)]. The interaction between waters surrounding the solute(s) (the hydration shell) and bulk water molecules leads to a relaxation process occurring on an intermediate time scale. The slowest relaxation process originates from the solute(s) and the interaction of the solute(s) with the first hydration shell and bulk water. The primary importance of the hydration shell is the exchange of shell and bulk waters; the self-contribution from bound water molecules is comparatively small. While in the alanine solutions the solute-water cross-terms are more important than the solute self-term, the solute contribution is larger in the dipeptide solutions. In the latter systems a much clearer separation of time scales between water and alanine dipeptide related properties is observed. The similarities and differences of the dielectric properties of the amino acid/peptide solutions studied in this work and of solutions of mono- and disaccharides and of the protein ubiquitin are discussed.

Thermodynamic and dielectric properties of aqueous solutions using ESIE charges to describe small solutes

Abstract The present paper describes molecular dynamics simulations of aqueous solutions with two solutes of different behaviour in water as formaldehyde and formamide. Lennard–Jones (12-6-1) type potentials obtained from ab initio MP2 level energies corrected with the superposition error basis set were employed to describe the solute–solvent interactions. The Coulomb interactions of these potentials were determined using several sets of solute atomic charges (in gas and solution phase), paying especial attention to the ESIE charges that reproduce the electrostatic component of the solute–water interaction energy. Some properties were evaluated to explain the effect of the solute on the thermodynamic ( U sol , U rel ,Δ H sol ), and dielectric ( e and τ ) response of the evolving medium. Small modifications to the traditional procedures were included in the calculations in order to improve the results.

Dielectric properties of aqueous solutions of α- d-glucose at 915 MHz

Using a cavity perturbation technique, dielectric properties of aqueous solutions of α- d-glucose at 915 MHz were investigated at concentrations varying from 10 to 70% (w/w) and temperatures ranging from 25–85°C. The dielectric constant increased with temperature but decreased with concentration, whereas the loss factor did the inverse. Dielectric properties for higher concentration glucose solutions showed the greatest variation at higher temperatures. Predictive models of the dielectric properties as functions of concentration and temperature were developed by stepwise regression. Such models are useful in estimating the volumetric heating of these solutions by microwave energy, studying the dielectric behavior of the glucose solutions, and chemical reactions involving glucose in aqueous solutions in a microwave field.

Predictive Equations for Dielectric Properties of NaCl, D‐sorbitol and Sucrose Solutions and Surimi at 2450 MHz

ABSTRACT: Variation in dielectric properties of aqueous solutions with different concentrations and ratios of NaCl, D‐sorbitol, and sucrose were investigated at 21 °C using the open‐ended coaxial probe technique at 2450 MHz. Several equations to estimate dielectric properties of mixed or pure solutions were formulated. The equations were tested with other concentrations of solutions and surimi as a food sample containing the solutes. The correlation between the new measured dielectric properties and the calculated values were analyzed using a General Linear Model. The resultant prediction equations are suitable for pure and mixed aqueous solutions of (0 to 6%) NaCl, (0 to 18%) D‐sorbitol and (0 to 60%) sucrose. For surimi, only loss factor was successfully predicted.

The dielectric relaxation in aqueous acetamide solutions

Based on the studies of SHF dielectric properties of aqueous solutions of acetamide in the temperature range 283–318 K and frequency range 3–26 GHz the dielectric relaxation parameters of the solutions were determined, and it was shown that the relaxation process is associated with the collective structural changes in water–nonelectrolyte network of bonds, during which the influence of hydrophilic interactions of polar groups and the effects of hydrophobic hydration almost completely counterbalance each other.

Dielectric study of aqueous solution of acetonitrile

Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous solutions of acetonitrile in temperature range of 0°C to 40°C. The calibration method based on the least squares fit method has been used. The excess permittivity, activation energy, Kirkwood correlation factor and activation energy of acetonitrile-water system have also been determined. The dielectric data show that acetonitrile molecules interact such that the dipoles have a tendency to remain antiparallel.

Dielectric Behavior of Aqueous Solutions of α,β-Poly(aspartyl hydrazide) and α,β-Poly(N-hydroxyethyl aspartamide): An Investigation of the Structural and Dynamic Properties

The dielectric properties of aqueous solutions of α,β-poly(aspartyl hydrazide) (PAHy) and of α,β-poly( N-hydroxyethyl aspartamide) (PHEA) were measured at 25 ° C in the frequency range of 100 MHz to 15 GHz using a time domain reflection method (TDR). Single time relaxation processes were found at 2 GHz and 15 GHz, respectively. The low frequency dispersion was inter preted in terms of the dynamics of polymeric segments based on the dielectric relaxation strength and the relaxation time. The high frequency process which is attributed to the rotational relaxation of water, indicated that water mole cules surrounding the polymeric backbone and in the pure state have a similar rotational behavior.

ChemInform Abstract: Dielectric Properties of Aqueous Solutions of Pyrazine (Ia) and Some of Its Alkyl Derivatives

ChemInform Abstract: Dielectric Properties of Aqueous Solutions of Pyrazine (Ia) and Some of Its Alkyl Derivatives

Dielectric properties of body tissues.

A review is given of the dielectric properties of various mammalian tissues and biological fluids for the frequency range from 1 Hz to 10 GHz. The properties considered are the frequency variations of the relative permittivity and electrical conductivity. An attempt has been made to present data which can be considered to be the most typical for each material. The dielectric properties of aqueous solutions of amino-acids, polypeptides, proteins, and then cells, are first outlined in order to lay the groundwork for the understanding of the properties of tissues. The electrical characteristics of various tissues and blood are presented in tabular and graphical form, and the differences between normal and cancerous tissue is also discussed. The effects of necrosis and temperature changes are described and the important contribution that water makes to the overall properties is emphasised. An insight into some of the dominant physiological and biophysical processes responsible for the dielectric properties of biological materials is also attempted, since this should aid further developments of both the diagnostic and therapeutic applications of radiofrequency and microwave radiation. Such information is also relevant to an understanding of the possible biological hazards of such radiation. The ways in which dielectric studies can aid an understanding at the molecular level of the basic physiological differences between normal and cancerous tissue, as well as of the physico-chemical state of biological water, are also described.

Microwave absorption in aqueous solutions of DNA.

In a recent Nature leading article the possibility of the occurrence of resonance absorption at microwave frequencies in DNA was discussed in terms of the latest available theoretical and experimental evidence, and its implications were assessed. Because of the far-reaching nature of these implications it is important that the existence or otherwise of such absorption be firmly established. Here we report on a concerted effort in two independent laboratories which has involved the measurement of the dielectric properties of aqueous solutions of circular DNA molecules in the frequency range 1-10 GHz. No resonance absorption or any form of enhanced absorption was demonstrated.

Dielectric Properties of Aqueous Solutions of Pyrazine and Some of its Alkyl Derivatives

Dielectric Properties of Aqueous Solutions of Pyrazine and Some of its Alkyl Derivatives

The dielectric properties of aqueous solutions of poly(ethylene glycol) and their influence on membrane structure

The dielectric constant of water is reduced drastically on addition of poly(ethylene glycol). The behaviour is not described by a linear mixture equation. The decreased dielectric constant can lead to the general perturbation of the membrane structure which is necessary in such a manner that a strong aggregation of membranes would lead to their fusion. The changed cation permeability in the presence of poly(ethylene glycol) can be expalained as the effect of the lowered dielectric constant on the transfer energy.

Dielectric properties of aqueous solutions of sonicated DNA above 40 MHz.

AbstractThe dielectric properties of sonicated calf‐thymus DNA sodium salt in aqueous solutions have been studied in the frequency range from 40 MHz to 2 GHz by time domain spectroscopy (TDS). A dielectric dispersion not previously reported was found, which has a characteristic frequency of about 150 MHz. All of the dielectric parameters are insensitive to the size of DNA fragments and to helix‐to‐coil transitions. The study of this dispersion as a function of DNA concentration and temperature allows us to conclude that it may be due to counterion fluctuation on short sections, probably in a direction transverse to the macromolecular axis.

Dielectric properties of solutions of oily materials solubilized by sodium dodecyl sulfate in aqueous solutions

The dielectric properties of aqueous solutions of a polar material and a nonpolar material solubilized by sodium dodecyl sulfate is described. The dielectric constant and ac electrical conductivity were measured in the frequency range from 110 to 1 MHz. The dielectric constants for the solubilized solutions show remarkable dependence on frequency. In the lower part of the frequency range, the dielectric constants increase with decreasing amounts of dissolved octanoic acid, while in the higher part of the frequency range the dielectric constants increase with increasing amounts of dissolved acid. On the other hand, the dielectric constants of solubilized solutions of n-octaine are not dependent on its concentration. Alternating current electrical conductivities at all frequencies are also dependent on the concentration of octanoic acid, but not dependent on the concentration of n-octane. The radius of a spherical particle with an electric double layer could be calculated through the measurement of dielectric constant and ac electrical conductivity. The radii of micelles penetrated by n-octane and octanoic acid molecules are large than that of the SDS micelle alone.

Dielectric Properties of Aqueous Solutions of Oily Materials Solubilized by Sodium Dodecyl Sulfate. II

The dielectric constant and A.C.electrical conductivity were measured in the frequency range from 110Hz to 1MHz. The dielectric constants for the solubilized solutions show remarkable dependence on frequency. In the lower frequency range, the dielectric constants increase with decreasing amounts of dissolved 1-octanol, while in the higher frequency range this dependence is reversed : the dielectric constants increase with increasing amounts of dissolved 1-octanol. A.C.electrical conductivities at all frequencies are also dependent on the concentration of 1-octanol. The radius of a spherical particle with an electric double layer could be calculated through the measurement of dielectric constant and the A.C.electrical conductivity. The radii of micelles penetrated by 1-octanol molecules are larger than those penetrated by octanoic acid or n-octane. The reduction of electrical conductivity of the solubilized micellar solutions is closely related to the change in the surface charge density of counterions of micelles resulting from the penetration by oily materials.

Molecular‐weight dependence of the low‐frequency dielectric properties of aqueous solutions of gel‐fractionated DNA

AbstractCombined three‐ and four‐terminal AC bridge measurements have been made at frequencies from 10 Hz to 100 KHz on samples of DNA with different molecular weight in aqueous solution under varying conditions of DNA concentrations and added salt. A method is described for the separation of large quantities of DNA fractionated according to size. A complicated pattern of dependence of the specific dielectric increment on concentration is found, and the difficulties of comparing the results from sample to sample are discussed. The dielectric properties of the fractionated samples of DNA in aqueous solution are reported for solutions sufficiently dilute that specific dielectric increment is independent of concentration. The specific dielectric increment of the solutions (with concentration measured in moles of DNA molecules/liter) is found to increase as the square of the molecular weight. The results are compared with results of polyelectrolyte theories which deal explicitly with counterion fluctuations and interactions. The frequency dependence of the dispersion is much broader than for simple Debye relaxation. It is satisfactorily fitted by the empirical Cole–Cole circular are function and the breadth of the dispersion is found to be, if anything, less for the fractionated samples than for native DNA in solution.

Structure and dielectric properties of aqueous solutions of formaldehyde and acetaldehyde

Structure and dielectric properties of aqueous solutions of formaldehyde and acetaldehyde

Dielectric studies on self-associating nucleosides and bases in aqueous solution.

Measurments have been made of the dielectric properties of aqueous solutions in which aggregates are formed by stacking. The nucleosides cytidine, uridine and thymidine, and the bases purine, pyrimidine and 6-methylamino-9-methyl-purine (N6,N9-dimethyladenine) were investigated at around 1 MHz, where the static increments can be determined, and for cytidine, dimethyladenine, uridine and pyrimidine measurements were also made in the 100-2000 MHz range where the main relaxation of the solute dipoles is found. Whereas cytidine and purine show a positive static dielectric increment increasing linearly with concentration, dimethyladenine, uridine, thymidine and pyrimidine show a similar negative effect. Also, within the experimental accuracy, single relaxation times are found for the solute dispersions investigated. It is suggested that these relaxations correspond to the effects of free rotation of individual polar molecules in the plane of stacking. This phenomenon would also account for the linear variation of the dielectric increments with concentration. These increments are thought to be positive or negative due to the varying balance in the solutions between the loss of polarization due to displaced and "bound" water and the corresponding gain due to the polarity of the solute molecules.